marmorstone



J1me 1955 R. J. MARMORSTONE 2,712,129

ANNUNCIATOR AND ALARM ST'STEM Filed Dec. 11, 1952 4 Sheets-Sheet 1 INVEN TOR.

E 5.55.2 2 ilffiiz'zzzarszane 1 4 K /mrs June 28, 955 R. J. MARMORSTONE2,712,129

- ANNUNCIATQR AND ALARM SYSTEM Ki wa j fl k z 4 Shee ts-Sheet s R. J.MARMORSTONE ANNUNCIATOR AND ALARM SYSTEM INVENTOR. EUbEIf :[Mzazvzzorz20272 June 28, 1955 Filed Dec. 11, 1952 fhfiib QORQBEBEE QMIKQ OR June28, 3955 Filed Dec. 11, 1952 R.'J. MARMORSTONE 2,712,129

ANNUNCIATOR AND ALARM SYSTEM 4 Sheets-Sheet 4 IN VEN TOR. ED15211:[Marzzzficslqne United States Patent ANNUNCIATOR AND ALARM SYSTEMRobert J. Marmorstone, Chicago, Ill., assignor, by mesne assignments,to.Panellit, Inc., Skokie, 11]., a corporation of Illinois ApplicationDecember 11, 1952, Serial No. 325,393

Claims. (Cl. 340-213) This invention relates to an electric alarm systemfor the supervision of a plurality of apparatuses and 2,712,129 PatentedJune 28, 1955 appear as the description proceeds, reference being had tothe accompanying drawings, in which:

Fig. 1 shows a circuit diagram of one form of the invention, allelements of the circuit being shown in the positions they assume it theapparatuses supervise by the alarm system are in normal condition;

more particularly to an alarm system of the kind wherein each of theapparatuses is provided with an annunciator whereas an alarm circuit iscommon to all the annunciators so as to be actuatable by any one ofthem. In such alarm systems each of the annunciators comprises anormally open signal switch which is closeable in response to adeviation from the normal condition in the apparatus to which theparticular annunciator is coordinated.

It is an object of this invention to provide an electric alarm system ofthe kind referred to which, while relatively simple in construction, isextremely reliable and inexpensive in operation. In particular, it is anobject of the invention to construct the alarm system in such a mannerthat there is no drain from the source of electric power during thenormal condition of the system.

It is another object of the invention to provide an alarm system of thekind referred to wherein each of the annunciator units contains twoalarm relays which interact with each other and with a master relaycoordinated to the common alarm signal in such a manner that those threerelays in their co-action control the duration of an energizing pulse soas to terminate that pulse when a certain sequence of operations of thethree relays has been completed.

Figs. 2 to 4 show different phases in the operation of the alarm systemof Fig. 1, those portions of the circuit which are active during theparticular phase illustrated in each figure being indicated by heavylines.

Referring first to Fig. l, the reference numeral 10 denotes a source ofdirect current, such as a l-volt battery, to which there are connected apositive lead (P) and a negative lead (N). For each of the apparatusesto be supervised by the alarm system there is provided an individualannunciator unit 11 comprising two I B by either of two other relaycoils H and T, the two contacts A1, A2,

In connection with an alarm system of the kind just mentioned it is anobject to provide a switch mechanism adapted to be triggered by themaster relay, one part of the switch mechanism being arranged in serieswith a contact controlled by the first alarm relay and another part ofthe switch mechanism in series with a contact controlled by the secondalarm relay, thereby to provide a temporarily closed path for the abovementioned energizing pulse to the master relay which becomes broken uponsaid second alarm relay becoming energized.

It is a further object of the invention to provide in an alarm system ofthe kind referred to a contact controlled by one of the two alarm relaysin a circuit controlled by the other of these two alarm relaysandfurther a contact controlled by the above mentioned master relay so thatthe first named alarm relay becomes operative only after the secondnamed alarm relay and also the master relay have become energized. i

' It is a further object of the invention to provide an electric alarmsystem of the kind referred to in which the individual signal which iscoordinated to each in dividual annunciator is adapted to displaysignals of dif-' ferent kinds depending on whether the signal has beenput into operation in consequence of a deviation from the normalcondition in the apparatus supervised by the particular annunciator orhas been reset manually.-

Preferably the individual alarm signal is in the form of a signal lampalternatively connectable into two circuits, of which one contains amotor-operable flasher latter belonging to a master control unit 22, areindicated by the same reference letter as is used for the coordinatedrelay coil but this reference letter is followed by an index number, e.g. A1 or B1. There are six to A6 coordinated to the relay coil A. Two ofthese six contacts, namely the contacts A5 and A6, form together adouble throw switch. The contacts A1, A2, A3, A4 and A5 are normallyopen; only the contact A6 is normally closed. Seven contact switches B1,B2, to B7 are actuatable by the relay coil B, of which the contacts B2,B3 and B6 are normally open. The contacts B1, B4, B5 and B7 are normallyclosed. The normally closed contacts B3 and B4 are united as amake-before-break continuity transfer contact device. This type ofcontact device operates in such a manner that the contact B4 staysclosed for a few milliseconds during which time the normally opencontact B3 closes.

Coordinated to each individual annunicator unit 11 are a signal switch12 responsive to changes of some selected condition in the connectedapparatus, which condition may be one of mechanical physical or chemicalnature, e. g. a change of level, pressure, temperature, acidity, etc.,and at least one signal lamp 13.

The relays A and B and their contacts A1 to A6 and B1 to B7 areconnected in the manner shown to eight common leads or buses, of whichtwo are the positive lead (P) and the negative lead (N), and the othersix are denoted by the reference'letters C, L, K, F, R and T.

' R, T, and (N), and-that all these annunciator units may be identicalto the illustrated device 11 with ated signal switch and lamp 12, 13.

'Common to all the individual annunciator. unit sysits associtems 11,12, 13 is a master alarm relay possessing a coil H and four contactswitches H1, H2, H3, and H4; Of

these four contacts, the contacts H2 and H3 are in the form of amake-before-break continuity transfer device of the kind above describedwith reference to the contacts B3 and B4. Between the contact H1 and thenega-.

tive lead (N) there is interposed an acoustical alarm 14, such as ahorn, and into a connecting lead 15 between the contact switch H1 andthe positive lead (P) there is inserted a normally closed push buttonswitch 16 for manually silencing the acoustical alarm 14.

Inserted into a lead 17 extending between the positive and the negativeleads (P) and (N) is the coil T of a testing relay which is arranged inseries with a normally open push button test switch 18. The testingrelay coil T controls two normally open contacts T1 and T2. The contactT1 is arranged in series with the acoustical alarm 14 by means of a lead19 connected to the lead (P). The contact T2 is connected btween thenegative lead (N) and the bus T which, in turn, is connected to thecontact B7 of each second alarm relay B. Mechanically coupled with aflasher motor F is a rotatable switch P1 electrically connected at itsone side to the negative lead (N) and at its other side through the busF to the contact A of each alarm relay A.

A normally closed push button switch 25) is inserted into a lead 21extending from the negative lead (N) to the bus C and thereby to eachalarm relay coil A. This switch 20 serves in a manner to be describedlater as a reset button for the signal lamps 13 and their controls.

The just described positions of the various contacts of the system ofthe invention are the positions these contacts assume when in none ofthe supervised apparatuses there exists a condition to which the alarmsystem is supposed to respond by an alarm signal. Fig. 1 shows that forthis condition none of the various circuits of the system is energized.Accordingly, there is no drain at all from the battery 19 during thenormal condition of the system.

If an abnormal condition occurs in any of the apparatuses supervised bythe alarm system so that the signal switch 12 coordinated to thatparticular apparatus closes, the elements of the individual annunciatorunit 11 coordinated to that apparatus and the elements of the masterunit 22 common to all the individual annunciator units 11 shift in thefollowing manner from the positions shown in Fig. 1 to the positionsshown in Fig. 2, in which they establish the circuits marked in Fig. 2by heavy lines: Closing of the signal switch 12 finds all the relays A,B, H and T initially unenergized and, in particular, finds the contactB1 closed. Consequently, a circuit is temporarily established extendingfrom (P), over 12, B1, coil A, and the push button switch 20 to (N).This circuit energizes the coil A and the energized coil A causes thecontact A1 to close and thereby to establish a holding circuit for thecoil A. With the coil A energized, the contacts A2, A3, A4, and A5close.

Of the now closed contacts A2, A3, A4 and AS the contact A2 remainsinefiective for the time being, no uninterrupted current path beingclosed as yet by said contact A2.

In contrast to the contact A2, the now closed contact A3 is in anuninterrupted circuit, namely in the circuit leading from (P) throughA3, the bus R, and the flasher motor F to the negative lead (N).Therefore, the motor F starts working, operating the flasher switch F1to open and close intermittently, thereby causing the signal lamp 13 toflash through bus F and contact A5.

Through the now closed contact switch A4 and the still closed contactswitch B5 there exists a circuit extending from the lead (P) through thebus L, the normally closed master continuity transfer contact H3, andthe relay coil H to the negative lead (N). This circuit energizes thecoil H with the effect that the positions of all the H-contacts becomereversed as compared with. their initial positions. The contact H1becoming thus closed, the horn 14 is in a closed circuit extending from(P) through 16, 15, H1 and 14 to (N) and, therefore, starts sounding(Fig. 3).

The contacts H2 and H3 being of the above mentioned make-before-breakcontinuity transfer type, the contact H3 opens only after a positiveperiod of time, such as one or,

two milliseconds, after the cutting-in of the relay coil H into acircuit (P), 16, 15, H2, H, (N) which is independent of the alarm relay11. This continuity transfer is provided to make sure that the coil Hremains sealedin through the contact H2 before the above described paththrough A4 and B5 breaks due to opening of the contacts H3 and B5.

By reason of the energization of the coil H, also the contact H4 changesits position so as to become closed. From Fig. 3 it will be seen thatthe closing of the contact H4 brings into play the alarm relay B over acircuit extending from (P) through A1, A2, B, B4 and H4 to (N). Thecontact B1 opens, so that possible fluttering of the signal switch 12has no influence on the coil A since the latter is locked in by thecontact A1. B2 closes, thus establishing a by-pass to the contacts A1and A2 for a purpose to be described later. Of the two contacts B3 andB4 of the make-before-break switch B3, 84, the contact B3 closes whileB4 is still closed for a few milliseconds after the cutting-in of thecoil 8 into circuit (P), A1, A2, B, B3 (N) which is independent of themaster relay 22.

Thus it will be seen that, when both the contacts A4 and B5 are stillclosed (Fig. 2), there is a pulse started to the coil H reaching thiscoil. via the bus L. This pulse is transferred to line 15, in order thatit may safely persist at least until the neutral feed for the B relayhas been established through the contact H4, that is until both relaycoils H and B have been rendered effective. Thus, the cutting in ofcoils H, B is positively based on the completion of the above describedparticular sequence of operations and not on a time constant, such asthat of an RC or other time constant network used in some prior artalarm devices.

As will best be seen from Fig. 4, the opening of the contact B4 breaksthe circuit through the closed contact H4, whereas the opening of thecontact terminates the positive feed to the H coil.

The contacts B6 and B7 are reversed in their positions withoutconsequence upon the circuit since the contact A6 is open at this time.

When the circuit is in the condition shown by Fig. 4. the acousticalalarm 14 sounds and that optical signal 13 which belongs to theparticular annunciator unit 11 shown in Fig. 4 also operates. Since thepurpose of the acoustical signal 14 is only to call. the attention ofthe attendant to the fact that there has occurred an irregularitysomewhere in the plant supervised by the alarm system and there shouldbe a fresh warning each time another of the various apparatuses goes outof order, it is desirable that the acoustical signal 14 be silenced assoon as its sounding has been recognized by the attendant. This isachieved by momentarily depressing manually the push button switch 16.This breaks the circuit through the relay H2 H and thereby through thecontract Hi. and horn 14. Permitting the push button 16 to return to itsnormally closed position will not re-establish the circuit for actuatingthe horn 14 since H2 remains open, H deenergized and H1 open until a newpulse arrives over the bus L. While the particular signal. switch 12whose closing caused the sounding of the horn 14 is still closed andwill remain closed until such time when the condi tion in the apparatuscoordinated to that particular switch 12 will have returned to normal,the circuits for and through the horn 14 remain broken at 85, H2 and Hi.(Only if another signal switch 12 would move into the I closed positionand thereby start in another of the annunicators the cycle of operationsabove described in connection with the illustrated annunciator 11, therewould then be again established a positive feed to the H relay throughthe corresponding contact B5, and the horn 14 would sound again. Whilethus the horn 14 is silenced, the aforementioned optical signal 13continues estates flashing, thereby indicating the particular apparatusthat went out of order.

To be ble to reset the optical signal 13 for a new actuation after theirregularity that caused the acoustical alarm 14 and the optical signal13 to go into action has been logged by the attendant, the lamp resetbutton 20 is provided. Depressing this button will deenergize the relaycoil A of the annunciator unit 11 (and through bus C of all the otherannunciator units). Since all the A contacts thereby return to thenormal position shown in Fig. 1, also the contacts A5 and A6 changetheir position so that the previously existing circuit containing theswitch F is interrupted and a new circuit for the optical signal 13 isestablished, extending from (P) through 13, A6 and B6 to (N). Thus,those annunciator units whose signal contacts 12 are closed willcontinue to display an optical signal which, however, is now not aflashing but a steady signal. Due to the mutual triggering of otherwiseindependent alarm and master relays 11, 22, the pushbuttons 16, 20 cansafely and effectually be operated in any desired sequence.

The relay B remains energized through the previously mentioned by-passcontact B2 regardless of A2 opening.

It is only when the signal switch 12 belonging to an energized signallamp 13 returns to its normal position, shown in Fig. 1, that also therelay coil B becomes deenergized, the contact B6 opens and thus thesignal lamp 13 goes out entirely.

It will be noted that the return of the signal contact 12 to its normalposition causes all elements of the coordinated annunciator unit 11 toautomatically return to their normal positions.

It will be apparent that the horn 14 is actuated by each signal switch12 which moves into closed position, provided the horn is silent at thistime. If an abnormalcy occurrs in a second apparatus while the horn isstill sounding in consequence of a previously occured abnormalcy inanother apparatus, the pressing of the push button switch 16 willsilence the horn 14 regardless of the fact that there had beenirregularities in two of the supervised apparatuses. However, the signallamps 13 of the annunciators coordinated to both these apparatuses willdisplay flashing signals, which flashing signals will change to steadyoptical signals upon operation of the reset button 20.

By means of the test push button 18 the acoustical signal 14 as well asthe optical signals 13 of all the annunciator units can be tested.Closing manually the normally open push button 18 energizes the testrelay coil T so that the two contacts T1 and T2 controlled by this coilclose;

contact T1 closes the circuit for the horn 14, and contact T2 thecircuit for the signal lamps 13 of all the annunciator units 11. Thus,the horn 14 sounds and all the signal lamps 13 of the system displaysteady visual signals.

While I have shown in the drawings one particular embodiment of myinvention, I desire it to be understood that various changes,modifications and re-arrangements of the elements of the circuit shownand described may be made without departing from the spirit of theinvention or from the scope of the appended claims.

I claim:

1. In an electric alarm system for the supervision of a plurality ofapparatuses each provided with an annunciator unit, an alarm circuitincluding a master relay common to all said annunciator units andarranged to be actuatable by any one of said annunciator units, each ofsaid annunciator units comprising a signal switch operable in responseto a deviation from the normal condition in the apparatus to which theparticular annunciator is coordinated and a first alarm relay controlledby said signal switch and a second alarm relay, said two alarm relayshaving each coil controlling a plurality of contacts, said second alarmrelay coil being arranged in a circuit containing a contact controlledby said first alarm relay coil and a contact controlled by said masterrelay coil so as to become operative only after said first alarm relayas well as said master relay coil have become energized.

2. In an electric alarm system for the supervision of a plurality ofapparatuses each provided with an annunciator circuit, a common masterrelay having an energization circuit extending through each annunciatorcircuit, each of said annunciator circuits comprising a signal switchoperable in response to a deviation from the normal condition of theassociated apparatus and a relay circuit, said relay circuit comprisinga first alarm relay which is actuated by the associated signal switch,the energization circuit of said master relay which extends through saidannunciator units including groups of contacts of said first and secondrelays connected in parallel and arranged to establish an energizationcircuit to said master relay coil upon the initial alarm actuation ofsaid first relay and to disestablish the energization circuit throughthe annunciator units when said second relay is de-energized, said relaycircuit also including a second relay having an energization circuitcontaining contacts controlled by said first relay and by said masterrelay which actuate said second relay when said master relay is actuatedby said first relay, a holding branch circuit for said master relay,circuit disconnect means responsive to operation of said second relayfor disconnecting the master relay from said annunciator circuits andconnecting the same to a holding branch circuit for holding the masterrelay in said actuated state, acknowledgment switch means for breakingsaid holding circuit, and audible alarm means responsive to theenergization of said master relay for sounding an audible alarm.

3. In an electric alarm system for the supervision of a plurality ofapparatuses each provided with individual annunciator circuits, a commonalarm circuit including a master relay having a first energizationcircuit including parallel sub-branches extending through each of saidindividual annunciator circuits, a condition-responsive sig-- nal switchfor controlling the operation of said first relay, said first and secondrelays having contacts in said subbranches of the energization circuitof said master relay and arranged to establish said energization circuitof said master relay when said first relay is operated in response to analarm position of the associated signal switch and to disestablish theenergization circuit through the associated annunciator circuit whensaid second relay is actuated, said master relay having contacts whichactuate said second relay when said master relay is actuated by saidfirst relay, said master relay having a make beforebreak continuitytransfer switch providing a normally closed contact path in series withsaid parallel subbranches of said annunciator circuits and a normallyopened contact path leading to a holding branch which parallels saidsub-branches of said annunciator circuits, said make-before-breakcontinuity transfer switch upon the actuation of said master relaytransferring connection of said master relay from said parallelsub-branches to said holding branch circuit, and switch means forbreaking said holding circuit.

4. In an electrical alarm system for the supervision of a plurality ofapparatuses each provided with an annunciator circuit, a common alarmcircuit including a master relay common to all of said annunciatorcircuits so as to be actuated by any one of said annunciator circuits,each of said annunciator circuits comprising a signal switch operableinresponse to a deviation from the normal condition in the apparatus towhich the particular annunciator circuit is coordinated and a first andsecond relay, said two relays controlling a plurality of contacts,contacts controlled by said first and second relays controlling theinitial operation of said master relay, said second relay arranged in acircuit containing contacts controlled by said master relay and saidfirst relay so as to become operative only after said first relay aswell as said master relay have become actuated, and switch mechanismtriggered by said master relay and being in series with said masterrelay and with said contacts controlled by said first and second relaysfor temporarily establishing an energization circuit to said masterrelay when a first relay is initially actuated, said contacts controlledby said second relay in said energization circuit of said masler relayoperating to break said energization circuit when said second relay isactuated following the actuation of said first relay and said masterrelay, and means for producing a signal announcement controlled by saidmaster relay.

5. The alarm system of claim 4 wherein said switch mechanism is amake-before-breal; continuity transfer switch which disconnects themaster relay from the energization circuit extending through saidannunciator circuits and connects the coil to a holding circuit which isindependent of said annunciator circuits when the master relay isinitially energized, and acknowledgment switch means for breaking saidholding circuit.

6. In an electrical alarm system for the supervision of a plurality ofapparatuses each provided with an annunciator circuit, a common alarmcircuit including a master relay common to all of said annunciatorcircuits so as to be actuated by any one of said annunciator circuits,each of said annunciator circuits comprising a signal switch operable inresponse to a deviation from the normal condition in the apparatus towhich the particular annunciator circuit is coordinated and a first andsecond relay, said two relays controlling a plurality of contacts,contacts controlled by said first and second relays controlling theinitial operation of said master relay, said second relay arranged in acircuit containing contacts controlled by said master relay and saidfirst relay so as to become operative only after said first relay aswell as said master relay have become actuated, each annunciator unitadditionally including a normally closed section of a make before-breakcontinuity transfer switch which section is in circuit with saidcontacts controlled by said master relay, a normally open section ofsaid makc-before-break continuity transfer switch connected to a holdingcircuit which by-passes said contacts controlled by said master relay,said normally open section of said latter makebefore-break continuitytransfer switch controlled by the associated second relay and arrangedto close upon the actuation of said second relay which follows theactuation of said first relay and said master relay, annunciator meansfor producing a first and a second signal announcement, the contacts ofsaid first and second relay arranged in circuit with said annunciatormeans for effecting said first announcement when said first relay isinitially actuated and for providing said second announcement when saidfirst relay is returned to its normal position and said second relayremains in its initial actuated position, and resetting means foractuating said first relay to its normal position without affecting saidsecond relay.

7. In an electric alarm system for the supervision of a plurality ofapparatuses each provided with an annunciator circuit, each of saidannunciator circuits comprising a signal switch operable in response toa deviation from the normal condition in the apparatus to which theparticular annunciator circuit is related, a signal lamp, a motoroperable flasher switch, a first and second alarm relay, said relaysboth operated in response to said operation of said signal switch, amanually operable switch arranged to return said first relay to itsnormal position, said signal lamp being alternatively connectable intotwo circuits, one of said two circuits containing said flasher switchand normally open contacts controlled by said first alarm relay forcausing said signal lamp to display a flashing signal upon initialoperation of said first relay and the second of said two circuitscontaining a normally closed set of contacts controlled by said firstrelay and a normally open contact controlled by said second relay forcausing said signal lamp to display a steady signal upon operation ofsaid manually operable switch.

8. In an electric alarm system for the supervision of a plurality ofapparatuses each provided with an annunciator circuit, an alarm circuitincluding a master relay common to all of said annunciator circuits soas to be actuatable by any one of said annunciator circuits, each ofsaid annunciator circuits comprising a normally open signal switchcloseable in response to a deviation from the normal position in theapparatus to which the particular annunciator is coordinated and a firstand a second relay, said first relay connected in series with saidsignal switch so as to be energized upon the closing thereof, saidmaster relay being in circuit with contacts of said first relay whichare arranged to energize said master relay upon the energization of saidfirst relay, said second relay arranged in a circuit containing contactscontrolled by said master relay so as to become operative only aftersaid first relay as well as said master relay have become energized,means for holding the energization of said master relay independently ofthe position of the signal switch, means for holding the energization ofthe first relay independent of the position of the signal switch, meansfor holding the energization of said second relay so long as the signalswitch is closed, a first alarm device actuated upon the energization ofsaid master relay, a manually operable acknowledgment switch fordeenergizing said master relay separately from the other relays, meansfor providing a first and a second condition-indicating signalcontrolled by said first and second relays, said last-mentioned meansproviding a first signal indication when said first relay is energizedand providing another signal indication when said second relay isenergized and said first relay is de-energized, and reset switch meansfor de-energizing said first relay independently of said second relay.

9. An annunciator system comprising a common alarm, a number ofannunciator circuits associated respectively with respective mechanismsto be monitored, each of said annunicator circuits including a pair ofrelays and a signal switch, a source of energizing potential, meansconnecting said first relays in circuit with the associated signalswitch and said source of energizing potential, means connecting saidmaster relay to said source of energizing potential through a number ofparallel branches each comprising contacts of said first and secondrelay arranged to couple said source of energizing voltage to saidmaster relay for a time interval which begins when the first relay isinitially actuated by said signal switch and terminates when said secondrelay is actuated, means connecting each second relay to said source ofenergizing potential through contacts of said master control relay andcontacts of the associated first relay arranged to actuate the secondrelay following the actuation of said first relay and said master relay,and alarm means controlled by said master relay.

l0. Annunciator apparatus comprising a group of annunciator circuits forindicating the condition of respec tive variables, each of saidannunciator circuits including a first and a second relay and a signalswitch, each of said first relays being controlled by the associatedsignal switch, a common alarm device, a master relay for controllingsaid common alarm device, contacts of said master relay arranged toenergize the audible alarm while the master relay is energized, meansconnecting said master relay to a source of energizing potential throughtwo parallel branches, one of the branches comprising a holding circuitincluding holding contacts controlled by the master relay in series witha normally closed acknowledgment switch, the other branch circuitincluding a series of parallel sub-branches each including normallyclosed contacts of one of said first relays in series with a set ofcontacts of the associated second relay, the contacts in saidsub-branches arranged to establish said other branch circuit when thefirst relay is operated by said signal switch in response to an abnormalcondition of the associated variable and to disestablish said branchcircuit through the corresponding sub-branch when the associated secondrelay is initially operated, means for initially operating each of saidsecond relays comprising contacts of said master relay in series withcontacts of said first relay which actuate said second relay when saidmaster relay is energized and said first relay is initially operated bysaid signal switch, and said contacts controlled by said master relay insaid first and second branches of said energization circuit comprising amakebefore-break continuity transfer switch arrangement wherein themaster relay is transferred from connection with said first branchcircuit to said second holding branch circuit upon energization of saidmaster relay.

References Cited in the file of this patent UNITED STATES PATENTSRichardson et al June 19, 1928 Bellamy June 19, 1928 Muehter Apr. 7,1942 Kennelly Apr. 13, 1948 Proctor Jan. 3, 1950 Sperry Mar. 28, 1950Seaton June 10, 1952

